Does sight influence the spells? I mean, if you can't see the whole target, should a GM add you a few misfortune dice? What do you think?

AFAIK there is no specifics on this. I would definately put it int he GM hands on what to add depending on the situation.

For example is the bright mage wanted to flameblast a group of goblins in the forest. I would definatley add misfortuen dice to represent the cover the goblins had from the blast. Where as if they were out in the open, then the squigs can eat cooked goblin.